Self-sealing injection device for thermoplastic material

ABSTRACT

The present invention relates to an injector device for injecting thermoplastic material. The device comprises a dispenser ( 8 ) feeding a transit passage ( 12 ) of an injector nozzle ( 7 ) with thermoplastic material, said passage opening out into the mold cavity ( 2 ) and being capable of being closed by a sliding needle ( 21 ). The needle ( 21 ) presents an extender ( 24 ) which passes through the dispenser ( 8 ) into ambient air via guide means ( 38 ) in order to co-operate with controlled means ( 30 ) for moving the needle ( 21 ). Sealing is provided between the extender ( 24 ) and the guide means ( 38 ) by the thermoplastic material itself, which material leaks between them from the dispenser ( 8 ) and accumulates in an annular groove ( 43 ) in one of them. The invention is applicable to injection molding devices.

[0001] The present invention relates to an injector device for injectinga thermoplastic material into a mold cavity, the material being in thefluid state when raised to a temperature that is not less than adetermined limit temperature higher than the temperature of ambient air,said injector device including:

[0002] a dispenser suitable for being maintained at an injectiontemperature higher than said determined limit temperature and defining athermoplastic material dispensing passage having at least one outlet fordelivering thermoplastic material in a determined longitudinal directionto one side of the dispenser;

[0003] an injection nozzle which is suitable for being maintained at aninjection temperature higher than said determined limit temperature andsituated on said side of the dispenser, being secured thereto, anddefining at least one longitudinal transit passage for the thermoplasticmaterial, said passage being placed in fluid-flow connection with theoutlet from the dispenser in the direction that is opposite to saiddirection and opening out in said direction in a front face suitable forbeing integrated in the mold cavity;

[0004] at least one longitudinal closure needle mounted to slidelongitudinally inside the transit passage between a position in which itcloses it and a position in which it opens it, and presenting alongitudinal extender extending in the direction opposite to saiddirection, passing through the dispenser into ambient air on the side ofthe dispenser that is longitudinally opposite from said side thereof,via means for guiding longitudinal sliding and presented securely by thedispenser for this purpose, going longitudinally away from said outlet,the guide means and the extender of the needle presenting respectiveinner and outer cylindrical longitudinal peripheral faces in mutualguiding contact for relative longitudinal sliding, with one of saidperipheral faces presenting an annular transverse groove for receiving asealing gasket relative to the other one of said peripheral faces in theclosed and open positions of the closure needle, and also in alllongitudinal positions between them; and

[0005] controlled means for causing the closure needle to slidelongitudinally between said closed and open positions, said controlledmeans being disposed in ambient air on the side of the dispenser that islongitudinally opposite from said side thereof, and being functionallyconnected to the extender of the closure needle.

[0006] Such a device is well known in numerous embodiments, for examplethat described in French patent application No. 00/03892 filed on Mar.28, 2000 by the Applicant, which describes various embodiments suitablefor providing determined positioning of the front face of the injectionnozzle, in particular in association with various ways of assembling itsecurely with the dispenser and various ways of assembling the variouscomponents of the injection nozzle relative to one another.

[0007] Nevertheless, until now, achieving sealing between the extenderof the closure needle and the means for guiding said extender in slidingrelative to the dispenser have remained problematic, particularlybecause of the difficulty in finding sealing gaskets that are capable ofremaining effective over time, given their simultaneous exposure totemperatures close to the injection temperature, given their progressiveclogging with thermoplastic material in the fluid state, and given theneed to use said gaskets to compensate for differences in transversethermal expansion between the extender of the closure needle and theguide means.

[0008] The object of the present invention is to provide a seal which issatisfactory in all those respects, and for this purpose the presentinvention proposes an injector device of the type specified in thepreamble, characterized in that said groove is offset longitudinallyrelative to the dispensing passage in the direction opposite to saiddirection by a distance (d) that is determined in such a manner thatunder the effect of ambient air thermal conduction causes it to beplaced at a temperature which is lower than the injection temperaturebut higher than said determined limit temperature when the dispenser andthe injection nozzle are maintained at the injection temperature, andthe thermoplastic material leaking in the fluid state between said innerand outer peripheral faces reaches said groove, fills it, and presentsviscosity therein such as to remain stopped therein and itselfconstitute the sealing gasket.

[0009] A person skilled in the art will readily understand that usingthe thermoplastic material itself as the sealing gasket between theouter peripheral face of the extender of the closure needle and theinner peripheral face of the guide means for guiding said extender inlongitudinal sliding relative to the dispenser makes it possible toobtain sealing that is effective and long-lasting, being intrinsicallyinsensitive to the temperature rise to which the guide means and theextender of the closure needle are subjected during an injectionoperation or to any risk of being damaged by the thermoplastic materialin the fluid state since that is what provides the sealing. The groovein one of the peripheral faces between which sealing is thus establishedthen acts relative to the thermoplastic material both as a supplyenabling sealing to be maintained even in the event of a thermalexpansion difference between said faces, thereby accommodating saiddifferences, and as means stopping any tendency to migrate beyond saidfaces.

[0010] More generally, as in the prior art, said inner and outerperipheral faces and said groove are circularly symmetrical about acommon longitudinal axis and/or said groove is arranged in the innerperipheral face of the guide means, although other transverseconfigurations of said peripheral faces, e.g. polygonal or plano-convex,can be suitable, particularly when a plurality of closure needles arejuxtaposed in multi-material injector devices, and matching shapes forthe groove can also be selected, without any of that going beyond theambit of the present invention.

[0011] To enable the required temperature to be obtained in the groovewhile occupying as little space in the longitudinal direction aspossible, i.e. in order to facilitate ambient air cooling of the innerperipheral face of the guide means and of the outer peripheral face ofthe extender of the closure needle, it is preferable to provide for theguide means to comprise a longitudinal sleeve which is placed on theside of the dispenser that is longitudinally opposite from said sidethereof, and connected to the dispenser, so as to project from thedispenser in the direction opposite to said direction, defining part ofsaid inner peripheral face and placed in contact with ambient air, inparticular transversely opposite said inner peripheral face. It is thenadvantageous for said groove to be arranged in the portion of said innerperipheral face which is defined by the sleeve.

[0012] For the same purpose, it is also preferable to provide for thecontrolled means to cause the closure needle to slide longitudinallybetween its closed and open positions to comprise a longitudinal annularactuator placed around the sleeve, leaving continuous annular clearancerelative thereto, and comprising both a cylinder secured to thedispenser and a piston constrained longitudinally to move with theextender of the closure needle. The use of an annular actuator, which isknown per se, provides the advantage that is likewise known of reducinglongitudinal size; however it also provides an advantage that isspecific to a device in accordance with the invention whereby preservingcontinuous annular clearance between its piston and the guide sleevemakes it possible to dispose a cushion of ambient air around the sleeve,thereby making it easier to cool the sleeve in the vicinity of thegroove that receives the thermoplastic material.

[0013] Other characteristics and advantages of the present inventionappear from the following description relating to a non-limitingembodiment, and from the accompanying drawing which forms an integralportion of the description.

[0014] Sole FIG. 1 shows a portion of a device of the invention forinjecting thermoplastic material in the fluid state into a mold cavity,part of the figure being in section on a plane that includes alongitudinal axis of an injection nozzle forming part of the device.

[0015]FIG. 1 shows a mold 1 defining a mold cavity 2 by means of a face3. An injection well 5 is provided in the mold 1 on a longitudinal axis4 occupying a predetermined position relative to the mold 1. The well 5opens out both into the face 3 in a longitudinal injection direction130, and into a face 6 of the mold 1, opposite from the face 3 along theaxis 4, in a longitudinal direction 131 opposite to the injectiondirection 130.

[0016] The inside of the well 5 receives a coaxial injection nozzle 7that is carried securely and releasably by a dispenser 8 of material tobe injected, which material is raised to and maintained at an injectiontemperature higher than a determined limit temperature referred to asthe “visco-elasticity temperature”, itself higher than the temperatureof ambient air, and being the temperature above which the thermoplasticmaterial is in the fluid state, such that said material is raised to andmaintained in a plastic state prior to being introduced into thedispenser 8 by means that are not shown, and until it reaches the cavity2 via the injection nozzle 7.

[0017] The dispenser 8 is mounted on a support plate 9 which essentiallyoverlies the dispenser 8 beside its side that is longitudinally remotefrom the mold 1, and that is fixed to the face 6 of the mold by meansthat are not shown, under conditions such that the dispenser 8 canexpand relative to the support plate 9 and to the mold 1 while itstemperature is rising at the beginning of an injection operation underconditions that are suitable for ensuring that the nozzle 7 and theinjection well 5 remain coaxial while the dispenser 8, the mold 1, andthe support plate 9 are stabilized at the temperature they presentduring the injection process.

[0018] Below, it is assumed that these conditions are satisfied, i.e.that the nozzle 7 is coaxial in the well 5 so that the well axis 4 canconsequently be considered as being the same as the axis of the nozzle7.

[0019] Methods of mounting the dispenser 8 to the support plate 9 on theface 6 of the mold to achieve this purpose are known to the personskilled in the art and lie outside the scope of the present invention,so they are not described in further detail.

[0020] The dispenser 8 carries the nozzle 7 via a nozzle-mountingsupport 10, which support defines a passage 25 angled at 90° to providefluid connection between a transverse passage 11 for dispensing materialin the plastic state as provided in the dispenser 8 which has an outletdefined by the angled passage 25 to lie on the axis 4 facing in theinjection direction 130 on the side of the dispenser 8 that facestowards the mold 1, and a longitudinal passage 12 for material in theplastic state extending in the injection direction 130 from theabove-defined outlet to the inside of the cavity 2. This transit passage12 is provided in the nozzle 7 along the axis 4 and opens out on saidaxis into the side of the cavity 2 via a front face 13 of the nozzle 7that faces in the injection direction 130.

[0021] The nozzle-mounting support 10 is engaged along the axis 4 in thedispenser 8 which is pierced right through for this purpose along theaxis 4 by a hole 14 that crosses through the passage 11, such that aportion of the hole 14 is to be found on either side of the passage 11.

[0022] The nozzle-mounting support 10 is engaged snugly in the hole 14and is retained securely but removably on the dispenser 8 by thedispenser being clamped longitudinally between an annular transverseflange 15 presented by the support 10 on the same side of the dispenser8 as the mold 1, the cavity 2, and the nozzle 7, and a transverse ring16 screwed coaxially onto a thread (not referenced) presented by thesupport 10 on the other side of the dispenser 8.

[0023] Such a configuration is described in the French patentapplication filed on Mar. 28, 2000 under No. 00/03892 by the Applicant,and as a result does not require any further description.

[0024] In a manner which is also described in the above-cited Frenchpatent application and which is therefore described herein only as sofar as it assists in understanding the present invention, the nozzle 7is essentially constituted by a cohesive but removable assembly of aplurality of components, and in particular a nozzle cylinder 17 whichcan be made integrally with the support 10 or which can be cohesivelybut releasably secured thereto, and a nozzle endpiece 18 which followsthe nozzle cylinder 17 in the injection direction 130 and which connectsthe nozzle cylinder 17 to the cavity 2, and in particular defines thefront face 13.

[0025] The general shape of the nozzle cylinder 17 is that of a tubeabout the axis 4 defining the passage 12 about said axis over the majorportion of the longitudinal dimension of the nozzle 7. Relative to thenozzle cylinder 17, the endpiece 18 constitutes a portion tapering inthe injection direction 130 both on the outside for connection to thecavity 2 via a transversely narrowed zone of the injection well 5,immediately adjacent to the face 3 with which the front face 13 becomescompletely flush, and on the inside so as to define a transverselynarrowed outlet 19 in the face 13 leading from the passage 12 into thecavity 2. Slightly set back in the direction 131 from the outlet 19 andfrom the face 13, the endpiece 18 defines an annular transverse shoulder20 around the passage 12 and facing in the direction 131, which shouldermay be frustoconical in shape, for example, being circularly symmetricalabout the axis 4 and tapering towards the outlet 19 in the injectiondirection 130 so as to form a sealing seat for a longitudinal closureneedle 21 which is received coaxially inside the passage 12, beingguided to slide longitudinally relative to the cylinder 17 and to theendpiece 18 of the nozzle 7 so as to be capable of controlled movementrelative thereto longitudinally between a position in which it closesthe passage 12 at the endpiece 18, as shown in the left-hand half ofFIG. 1, and a position in which it opens the passage 12, specifically atthe endpiece 18, as shown in the right-hand half of FIG. 1.

[0026] The shape of the closure needle 21 is itself known, and matchesthe shape of the endpiece 18 so as to define the states in which thepassage 12 is opened and closed by said endpiece.

[0027] In the example shown, the needle 21 has a front face 22 facing inthe injection direction 130 and which, in the closed position, comesflush with the front face 13 of the endpiece 18, itself lying flush withthe face 3 of the cavity 2 when the mold 1, the nozzle 7, the dispenser8, and the support plate 9 are stabilized at the temperature they are tohave during the injection process, whereas when in the open positionthis front face 22 is retracted in the direction 131 away from theshoulder 20. The shapes of the front faces 22 and 13 and the directionin which they face relative to the axis 4 are associated with the shapeof the face 3 of the cavity 2. In the example shown, they are both planeand perpendicular to the axis 4 as is the face 3 of the cavity 2, butthey could equally well present a shape other than plane and/or beoriented obliquely relative to the axis 4.

[0028] Set back in the direction 131 from the face 22, the needle 21presents a transverse annular shoulder 23 facing in the same directionas the face 22, which shoulder 23 presents a cone angle identical tothat of the shoulder 20 against which it presses in a mutual sealingrelationship when the needle is in the closed position, whereas it isset back from said shoulder 20 in the direction 131 when the needle isin the open position. Between the face 22 and the shoulder 23, theneedle 21 is defined by an outer peripheral face that is not referenced,and that in the closed position matches an inner peripheral face,likewise not referenced, presented by the endpiece 18 between theshoulder 20 and the face 13 to define the passage 12 in the immediatevicinity of the outlet 19, thereby likewise establishing sealing betweenthe closure needle 21 and the endpiece 18 in this location when in theclosed position.

[0029] In a variant that is not shown, sealing between the closureneedle 21 and the endpiece 18 in the closed position can be providedsolely by mutual contact between the shoulders 20 and 23 or by mutualcontact between the outer peripheral face of the closure needle 21 andthe inner peripheral face of the endpiece 18 in the immediate vicinityof the outlet 19. Other arrangements could equally well be selected forthis purpose without thereby going beyond the ambit of the presentinvention.

[0030] Set back in the direction 131 from the shoulder 23, the needle 21presents a shape that is likewise known per se, suitable for leaving anempty cross-section around the needle inside the passage 12 that islarge enough to enable the thermoplastic material in the fluid state tobe delivered from the passage 11 through the outlet 19. Any suitablemeans can be provided in this location between the nozzle cylinder 17and the closure needle 21 to ensure both that the needle remains coaxialrelative to the passage 12 and that the needle 21 is guided inlongitudinal sliding relative to the nozzle cylinder 17 between theclosed and open positions of the outlet 19 in the endpiece 18.

[0031] Furthermore, longitudinally opposite from its front face 22, theclosure needle 21 is guided to slide axially in the nozzle-mountingsupport 10 by a coaxial extender 24 into which it is screwed coaxiallyor with which it is secured by any other means, preferably releasably,in a zone of the passage 12 that is situated longitudinally oppositefrom the outlet 19, i.e. in the immediate vicinity of the angled passage25 connecting the passage 12 to the passage 11 of the dispenser 8.

[0032] The extender 24 passes through the nozzle-mounting support 10 andpresents outside the dispenser 8, opposite from the nozzle 7 along theaxis 4 an end 26 into which there is screwed securely but releasably abolt 27 for releasably securing a transverse washer 28 that iscircularly symmetrical about the axis 4 serving to provide a connectionfor transmitting movement in longitudinal translation generated by apiston 29 of a double-acting hydraulic actuator 30. The actuator 30 alsocomprises a cylinder 31 releasably secured, e.g. by bolts, to acorresponding zone of the support plate 9 so that when its piston 29 iscaused in move in longitudinal translation relative to its cylinder 31that acts via the washer 28 either to pull on the end 26 along the axis4 in the direction 131 so as to move the end 26 away from the face 13 ofthe endpiece 18, thereby moving the closure needle 21 into its positionfor opening the passage 12 to the cavity 2, or else to push the needle21 in the opposite direction 130 so as to bring it into its position forclosing the passage 12 in the endpiece 18.

[0033] In order to receive the cylinder 31 of the actuator 30longitudinally opposite from the dispenser 8 and also to enable theextender 24 of the closure needle 21 to pass through under conditionssuitable for enabling the end 26 of the extender 24 to co-operate viathe washer 28 with the piston 29 of the actuator 30, said zone of thesupport plate 9 is pierced by a through hole 32 along the axis 4, saidhole being defined facing the axis 4 by three inside peripheral faces33, 34, and 35 which are circularly cylindrical about an axis that isassumed to coincide with the axis 4, having diameters of increasing sizewith the faces 33, 34, and 35 following one another in that order in thedirection 131 and being interconnected in pairs by plane transverseannular shoulders 36, 37 facing in said direction 131. It can be seenthat the axis of the hole 32 could nevertheless be offset transverselyto a small extent relative to the axis 4 given the differences inthermal expansion that can arise between the support plate 9 and thedispenser 8 carrying the nozzle-mounting support 10 which acts inparticular via a tubular sleeve-forming portion 38 described below toguide the extender 24 of the injection needle 21 in longitudinal slidingalong the axis 4 and thus to define the position of said axis 4. While athermoplastic material in the fluid state is being infected; thedispenser 8 is raised to a temperature that is higher than that of thesupport plate 9, which is much more exposed to ambient air and isconsequently better cooled thereby.

[0034] By means of the hole 32 shaped in this way, the nozzle-mountingsupport 10 extends in the direction 131 inside said zone of the supportplate 9 by means of the tubular sleeve-shaped portion 38 which isdefined going away from the axis 4 by an outer peripheral face 39 thatis circularly symmetrical about said axis and that has a diameter thatis perceptibly smaller than the diameter of the inner peripheral face 33of the hole 32 and also than the diameter of the unreferenced thread onthe nozzle-mounted support 10 that receives the ring 16. In thedirection 131, this face 39 is connected to a plane annular front face40 that is circularly symmetrical about the axis 4 and that isperpendicular thereto, which face 40 faces in said direction 130 and issituated at an intermediate level of the inner peripheral face 35 of thehole 32.

[0035] Between this front face 40 and the angled passage 25, thenozzle-mounting support 10 including the sleeve-shaped portion 38 isdefined towards the axis 4 by an inner peripheral face 41 that iscircularly cylindrical about the axis 4. The extender 24 of the closureneedle 21 is placed in guiding contact for longitudinal sliding relativeto said face 41 via an outer peripheral face 42 which is likewisecircularly cylindrical about the axis 4, having a diameter that issubstantially identical to that of the face 41, and defining theextender 24 of the closure needle 21 going away from the axis 4, fromthe connection of said extender 24 with said needle 21 all the way tothe end 26 of said extender 24. Longitudinally, the extender 24 isdimensioned in such a manner that both in the position of the closureneedle 21 corresponding to the passage 12 being closed and in itsposition corresponding to said passage being opened, the end 26 of theextender 24 is continuously situated outside the sleeve-forming portion38, i.e. it projects relative to the front face 40 in the direction 131while the connection between the extender 24 and the needle 21 remainsinside the passage 12 or the angled passage 25.

[0036] In order to seal the faces 41 and 42 relative to thethermoplastic material traveling in particular in the passages 12 and25, the face 41 has at least one groove 43 formed therein suitable forreceiving a sealing material, it being understood that the co-operationbetween the nozzle-mounting support 10 and the dispenser 8 also providessealing relative to the thermoplastic material in the fluid state oneither side of the passage 11.

[0037] In accordance with the present invention, this sealing materialis constituted by the thermoplastic material itself, which leaks fromthe angled passage 25, penetrating between the faces 41 and 42 andmigrating between them in the direction 131, coming to rest in thegroove 43 and accumulating therein, given firstly thelongitudinally-determined position thereof and secondly the fact that itis at a temperature that is lower than the injection temperature. Thegroove 43 is subjected to cooling by heat being conducted through thesleeve-forming portion 38 and along the extender 24 of the closureneedle 21 in the direction 130, because the sleeve-forming portion 38 isexposed to ambient air via its face 39 and 40, and because the end 26 ofthe extender 24 and its portion adjacent thereto situated outside thesleeve-forming portion 38 is also exposed to ambient air, whereas theportion of the extender 24 situated inside the angled passage 25 and theportions of the nozzle-mounting support 10 defining said angled passage25 are exposed to the injection temperature at which the thermoplasticmaterial is maintained inside the dispensing passage 11 and the transitor injection passage 12, thus tending to heat the groove 43 by heatbeing conducted in the direction 131 along the nozzle-mounting support10 and the extender 24 of the closure needle 21.

[0038] The size and the longitudinal position of the groove 43 withinthe sleeve-forming portion 38, relative to the angled passage 25 and thedispensing passage 11, i.e. the longitudinal distance d between thegroove 43 and the passages 11 and 25, can readily be determined by theperson skilled in the art using competences that are normal in the art,as a function in particular of the thermal conduction coefficient of thematerials constituting the sleeve-forming portion 38, thenozzle-mounting support 10, and the extender 24 of the closure needle21, on the basis of their respective shapes and sizes, on the basis ofthe range of injection temperatures that are liable to be used for thethermoplastic material, given the nature thereof, on the basis of theway in which the viscosity of said thermoplastic material varies, or onthe basis of a determined range of thermoplastic materials as a functionof temperature and as a function of a plausible range of temperaturesfor ambient air, such that the temperature to which the groove 43 israised during the injection process by equilibrium being achievedbetween the above-specified opposing effects of cooling and heating bythermal conduction, which temperature is intermediate between thetemperature of ambient air and the injection temperature, still remainshigher than the limit temperature at which the thermoplastic material isin the fluid state but is nevertheless far enough below the injectiontemperature for the viscosity of the material reaching the groove 43 topresent a value such that said thermoplastic material accumulates in thegroove 43 and remains therein, forming an annular gasket providingmutual sealing between the faces 41 and 42.

[0039] By way of non-limiting example, good results have been obtainedin testing by giving d a value that is about five times the diameter ofthe faces 41 and 42, with the longitudinal distance between the frontface 40 and the passages 11 and 25 (i.e. the sum of d, plus thelongitudinal size of the groove 43, plus the longitudinal distancebetween said groove and the front face 40) having a value of about sixtimes the above-specified diameter. Naturally, other proportions couldbe selected without thereby going beyond the ambit of the presentinvention, in particular as a function of the ease or otherwise withwhich a flow of ambient air can be established around the sleeve-formingportion 38 and the portion of the extender 24 of the closure needle 21that is adjacent to the end 26 of said extender.

[0040] In addition, in order to prevent the extender 24 of the closureneedle 21 turning about the axis 4 relative to the nozzle-mountingsupport 10 or to the cylinder 17 and the endpiece 18 of the nozzle 7,the sleeve-forming portion 38 presents a rectilinear slot 45 opening outinto the front face 40 and into the outer and inner peripheral faces 39and 41 in a mean plane that contains the axis 4, and a projection 44 isreceived in said slot 45 with the ability to slide longitudinally butwithout the ability to turn about the axis 4, said projection 44 beingintegrally connected to the extender 24 of the closure needle 21 orbeing implemented in the form of a pin which is secured to said extender24. The projection 44 extends perpendicularly to the axis 4 relative tothe outer peripheral face 42 of the extender 24 over a distance that isno greater than the thickness of the sleeve-forming portion 38 asmeasured between its faces 39 and 41, perpendicularly to the axis 4. Therespective longitudinal dimensions of the projection 44 and of the slot45 are such as to avoid constituting an obstacle to displacement of theclosure needle 21 together with its extender 24 between the opening andclosed positions, while preventing turning about the axis 4 in each ofthese extreme positions, and at any point between them.

[0041] In conventional manner, the actuator 30 is disposed coaxially inthe hole 32, i.e. it is at least approximately coaxial with the needle21, and its piston 29 is connected to the washer 28 which is secured tothe extender 24, itself secured to the injection needle 21 via atransmission member 46 which, while providing a connection without anyslack along the axis 4, nevertheless allows for relative displacement totake place perpendicularly to said axis so as to allow the hole 32 andthe actuator 30 to be slightly off-center relative to the nozzle 7,given the above-specified differences in thermal expansion between thesupport plate 9 carrying the cylinder 31 of the actuator 30 and thedispenser 8 carrying the nozzle-mounting support 10 which defines theposition of the axis 4.

[0042] Nevertheless, to simplify the description, it is assumed below,as assumed above with reference to the hole 32, that the actuator 30 iscoaxial with the nozzle 7, and more precisely is circularly symmetricalabout the axis 4 as described with reference to the hole 32.

[0043] The actuator 30 is shown in such a position in FIG. 1 to whichreference is made when describing the actuator, said description beingrestricted essentially to those characteristics of the actuator whichcorrespond to a preferred embodiment of the present invention.

[0044] From the FIGURE it can be seen that the actuator 30 is an annulartype actuator whose piston 29 and cylinder 31 are both circularlyannular about the axis 4.

[0045] Respectively going away from said axis and along said axis, thecylinder 31 is defined by respective outer and end peripheral faces thatare not referenced, enabling it to be engaged in a housing definedinside the hole 32 via its shoulders 36 and 37 and its inner peripheralface 34 and a portion of its inner peripheral face 35 directly adjacentto the shoulder 37, under conditions that are easily determined by theperson skilled in the art so as to ensure that the actuator cylinder 31is accurately positioned both longitudinally and transversely relativeto the support plate 9, and so as to ensure that the cylinder 31 is setback longitudinally inside the hole 32 relative to a face 54, e.g. aplane face that is perpendicular to the axis 4 and defining the supportplane 9 in the direction 131, i.e. longitudinally away from thedispenser 8, the nozzle 7, and the mold 1. In this face 54, a removablecover 55 protects the actuator 30 inside the hole 32.

[0046] Going towards the axis 4, the cylinder 31 presents two innerperipheral faces 66 and 68, both circularly cylindrical about the axis 4which they face, having the same diameter smaller than the diameter ofthe inner peripheral face 33 of the hole 32.

[0047] The faces 66 and 68 are spaced apart longitudinally in such amanner that the cylinder 31 defines between them an annular cavity 74that is circularly symmetrical about the axis 4, said cavity beingsealed in both directions 130 and 131 and also going away from the axis4.

[0048] The cylinder 31 uses the faces 66 and 68 to guide the piston 29in axial sliding.

[0049] To this end, the piston 29 has a rod 69 defined going away fromthe axis 4 by an outer peripheral face 70 that is circularly cylindricalabout the axis 4 with a diameter that is identical to the diameter ofthe faces 66 and 68 which are in sealing contact with the face 70, e.g.via appropriate sealing gaskets (not referenced) such that the rod 69 ofthe piston defines the annular cavity 74 of the cylinder 31 in leaktightmanner towards the axis 4.

[0050] Inside said cavity 74, the rod 69 carries a transverse plate 75that is circularly annular about the axis 4, projecting away from theaxis 4 from the face 70 of the rod 69. Going away from the axis 4, thetransverse plate 75 is defined by an outer peripheral face 76 that iscircularly cylindrical about said axis having a diameter that isidentical to the diameter of an inner peripheral face 58 of the cylinder31, likewise circularly symmetrical about the axis 4 and defining thecavity 74 going away from the axis 4. The face 76 is in sliding contactwith said face 58 and the plate 75 is sealed relative thereto, forexample by means of an appropriate sealing gasket (not shown).

[0051] Longitudinally, the plate 75 is of a size that is smaller thanthat of the cavity 74 so that the plate 75 subdivides the cavity inleaktight manner into two sealed chambers 80 and 81 that are circularlycylindrical about the axis 4, with the respective volumes of thechambers 80 and 81 varying in opposite directions as the plate 75 slidesin one direction or the other inside the cavity 74 relative to thecylinder 31, i.e. when the piston 29 moves longitudinally in onedirection or the other relative to said body 31.

[0052] The chambers 80 and 81 are offset respectively in the direction130 and in the direction 131 relative to the plate 75, and thedifference between the respective longitudinal dimensions of the plate75 and of the cavity 74 is equal to the longitudinal stroke that theclosure needle 71 needs to travel between its closed position in whichthe plate 75 comes into abutment in the direction 130 against thecylinder 31 inside the cavity 74, with the volume of the chamber 80 thenbeing at its minimum while the volume of the chamber 81 is at itsmaximum, and its open position in which the plate 75 comes into abutmentin the opposite direction 131 against the cylinder 31 inside the cavity74, with the volume of the chamber 81 then being at its minimum whilethe volume of the chamber 80 is at its maximum.

[0053] The face 70 of the rod 69 is itself dimensioned longitudinally oneither side of the plate 75 so as to remain projecting to some extent inthe direction 130 and in the direction 131 relative to the cylinder 31in both of the limit positions as defined above for the piston 39relative to the body 31.

[0054] In this respect, the longitudinal dimensions of those portions ofthe face 70 that are situated on respective sides of the plate 75 aremeasured respectively between the plate 75 and a plane transverse face84 that is circularly annular about the axis 4 facing in the direction130 and thus projecting in said direction 130 from the cylinder 31, andbetween the plate 75 and a plane transverse face 85 that is circularlyannular about the axis 4 and perpendicular thereto, which face 85 thusfaces in the direction 131 and projects longitudinally in the direction131 from the cylinder 31.

[0055] In order to have an assembly that is compact, the rod 69 of theactuator in the example shown is tubular in shape and is defined towardsthe axis 4 by an inner peripheral face 86 that is circularly cylindricalabout the axis 4 with a diameter that is greater than the diameter ofthe outer peripheral face 39 of the sleeve-forming portion 38 of thesupport 10 for mounting the nozzle 7 on the dispenser 8, and a priorithan the outer peripheral face 42 of the extender 24 of the closureneedle 21, thus making it possible to place the piston rod 69 around afraction of the sleeve-forming portion 38, as shown in FIG. 1.

[0056] The inner peripheral face 86 thus extends the face 84longitudinally to the immediate vicinity of the face 85 to which it isconnected by tapping 87 whereby the rod 69 of the piston 29 receivessecurely but releasably the member 46 for transmitting movement.

[0057] To this end, the member 46 is generally in the form of a circularannulus about the axis 4, and in particular it presents a portion 88 inthe form of a sleeve presenting, going away from the axis 4, a thread 89complementary to the tapping 87 and engaged therein.

[0058] The sleeve-forming portion 88 thus placed inside the piston rod69 is also defined going towards the axis 4 by an inner peripheral face90 that is circularly cylindrical about said axis having a diameter thatis smaller than the diameter of the inner peripheral face 86 but greaterthan the diameter of the outer peripheral face 42 of the extender 24 ofthe closure needle 21 such that there remains between the face 90 andthe face 24, and also between the face 86 and the faces 24 and 39,annular clearance 132 that is continuous both circumferentially andlongitudinally, enabling a limited amount of transverse movement to beaccommodated between the actuator 30 carrying the member 46 and theextender 24 of the closure needle 21 together with the sleeve-formingportion 38 of the nozzle-mounting support 10.

[0059] This continuous tubular clearance 132 that is open to ambient airvia the assembly clearances between the various components of theinjector device, and possibly also via passages specially provided forthis purpose, e.g. between the actuator cylinder 31 and the faces 34 to37 of the hole 32 (in a manner that is not shown but that is easilydesigned by a person skilled in the art), also serves to bring thisambient air into contact with the faces 43 and 41 of the sleeve-formingportion 38 and with the face 42 of the extender 24 of the closure needle21, in that portion of said face 42 that is situated projecting beyondthe sleeve-forming portion 38, thus contributing to cooling saidsleeve-forming portion 38 and the extender 24 in the groove 43, andconsequently cooling the thermoplastic material that reaches said grooveby migrating between the faces 41 and 42 from the angled passage 25, asdesired in the context of the present invention.

[0060] Inside the piston rod 69, the outer peripheral thread 89 isconnected to the inner peripheral face 90 via a plane transverse face 91that is circularly annular about the axis 4 and perpendicular thereto,said face 91 facing in the direction 130 as does the face 84 relative towhich it is set back slightly in the longitudinal direction inside therod 69 so as to leave longitudinal spacing relative to the face 40 ofthe sleeve-forming portion 38 of the nozzle-mounting support 10,regardless of the position of the piston 29 relative to the actuatorcylinder 31, within the limits determined by the plate 75 coming intoabutment against the cylinder 31 inside the cavity 74 in the directions130 and 131, so that longitudinal continuity of the clearance 132 isconserved regardless of the position of the piston.

[0061] Longitudinally away from its connection with the face 91, theouter peripheral thread 89 connects with a plane transverse shoulder 92that is circularly annular about the axis 4 and that is perpendicularthereto, said shoulder 92 facing in the same direction as the face 91and being placed longitudinally facing the face 85 of the piston rod 69.The shoulder 92 bears against said face 85 to limit screw-tightening andthe extent to which the sleeve-forming portion 88 can be engagedlongitudinally inside the piston rod 69.

[0062] At the shoulder 92, this sleeve-forming portion 88 is secured inthe direction 131 to a portion 133 of the transmission member 46 lyingoutside the piston rod 29 and generally in the form of a circularannular ring about the axis 4, towards which axis the ring defines inconventional manner an annular groove 134 about said axis.

[0063] In a manner well known to the person skilled in the art andtherefore not described, the washer 28 is received in said groove 134without any longitudinal clearance, but with transverse clearance in alldirections so that even though the piston 29 of the actuator 30 and theclosure needle 21 can move relative to each other transversely in alldirections, they nevertheless form a single unit for longitudinalmovement in one direction or the other.

[0064] To drive such movement, a hydraulic fluid can be inserted at willinto the chamber 80 or 81 in selective manner while exhausting anyhydraulic fluid that might be found in the other chamber, with saidchambers being connected for this purpose to a hydraulic fluid circuit(not shown) external to the actuator 30 via couplings such as 110 in amanner that is well known to the person skilled in the art and that istherefore not described.

[0065] The person skilled in the art will readily understand that theembodiment of the present invention described above constitutes merely anon-limiting example and numerous variants can be made thereto withoutgoing beyond the ambit of the invention. In particular, when there is noconcern or constraint on longitudinal size that have lead to the pistonrod of the actuator being implemented in tubular form, it is entirelypossible to adopt the characteristic dispositions of the invention inassociation with an actuator having a solid rod, without that goingoutside the ambit of the present invention.

1/ An injector device for injecting a thermoplastic material into a moldcavity (2), the material being in the fluid state when raised to atemperature that is not less than a determined limit temperature higherthan the temperature of ambient air, said injector device including: adispenser (8) suitable for being maintained at an injection temperaturehigher than said determined limit temperature and defining athermoplastic material dispensing passage (11) having at least oneoutlet (25) for delivering thermoplastic material in a determinedlongitudinal direction (130) to one side of the dispenser; an injectionnozzle (7) which is suitable for being maintained at an injectiontemperature higher than said determined limit temperature and situatedon said side of the dispenser (8), being secured thereto, and definingat least one longitudinal transit passage (12) for the thermoplasticmaterial, said passage being placed in fluid-flow connection with theoutlet (25) from the dispenser (8) in the direction (131) that isopposite to said direction (130) and opening out in said direction (130)in a front face (13) suitable for being integrated in the mold cavity(2); at least one longitudinal closure needle (21) mounted to slidelongitudinally inside the transit passage (12) between a position inwhich it closes it and a position in which it opens it, and presenting alongitudinal extender (24) extending in the direction (131) opposite tosaid direction (130), passing through the dispenser (8) into ambient airon the side of the dispenser (8) that is longitudinally opposite fromsaid side thereof, via means (38) for guiding longitudinal sliding andpresented securely by the dispenser (8) for this purpose, goinglongitudinally away from said outlet (25), the guide means (36) and theextender (24) of the needle (21) presenting respective inner and outercylindrical longitudinal peripheral faces (41, 42) in mutual guidingcontact for relative longitudinal sliding, with one of said peripheralfaces (41) presenting an annular transverse groove for receiving asealing gasket relative to the other one of said peripheral faces (42)in the closed and open positions of the closure needle (21), and also inall longitudinal positions between them; and controlled means (30) forcausing the closure needle (21) to slide longitudinally between saidclosed and open positions, said controlled means being disposed inambient air on the side of the dispenser (8) that is longitudinallyopposite from said side thereof, and being functionally connected to theextender (24) of the closure needle (21); the device being characterizedin that said groove (43) is offset longitudinally relative to thedispensing passage (11) in the direction (131) opposite to saiddirection (130) by a distance (d) that is determined in such a mannerthat under the effect of ambient air thermal conduction causes it to beplaced at a temperature which is lower than the injection temperaturebut higher than said determined limit temperature when the dispenser (8)and the injection nozzle (7) are maintained at the injectiontemperature, and the thermoplastic material leaking in the fluid statebetween said inner and outer peripheral faces (41, 42) reaches saidgroove (42), fills it, and presents viscosity therein such as to remainstopped therein and itself constitute the sealing gasket. 2/ An injectordevice according to claim 1, characterized in that said inner and outerperipheral faces (41, 42) and said groove (43) are circularlycylindrical about a common longitudinal axis (4). 3/ An injector deviceaccording to claim 1 or claim 2, characterized in that said groove (43)is arranged in the inner peripheral face (41) of the guide means (38).4/ An injector device according to any one of claims 1 to 3,characterized in that the guide means (38) comprise a longitudinalsleeve (38) which is placed on the side of the dispenser (8) that islongitudinally opposite from said side thereof and is secured to thedispenser (8), projecting from the dispenser (8) in the direction (131)opposite said direction (130), defining part of said inner peripheralface (41) and placed in contact with ambient air, in particulartransversely opposite from said inner peripheral face (41). 5/ Aninjector device according to claims 3 and 4, characterized in that saidgroove (43) is arranged in the portion of said inner peripheral face(41) which is defined by the sleeve (38). 6/ An injector deviceaccording to claim 4 or claim 5, characterized in that the controlledmeans (30) for causing the closure needle (21) to slide longitudinallybetween its closed and open positions comprise a longitudinal annularactuator (30) placed around the sleeve (38), leaving continuous annularclearance (132) relative thereto and comprising firstly a cylinder (31)secured to the dispenser (8) and secondly a piston (29) longitudinallysecured to the extender (24) of the closure needle (21).